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Development of a Quad-Rotor Biplane MAV with Enhanced Roll Control Authority in Fixed Wing Mode
Abstract and Figures
In order to ensure mission versatility, multi-role vehicles must be capable of vertical takeoff and landings as well as rapid forward flights. In all flight modes, these vehicles must also have robust control systems in place. In this study, one such hybrid air vehicle, called the quad-rotor biplane is considered. It consists of four proprotors with two wings oriented in a biplane configuration. It was observed during forward flight that the baseline vehicle configuration suffers from a lack of sufficient roll control authority. This paper explores the deficiencies of the installed roll control method and investigates several other suitable control systems. These include a pair of pivoting wing tips, thrust vectoring via angled proprotors, and a variable collective pitch proprotor method. Roll moments were measured in a 6.25 m/s wind via a torque gauge and measured as much as 97% above baseline system roll magnitudes. It was found that by combining the angled proprotor and variable collective control, a 186% improvement in control authority could be achieved with an added benefit of improving the forward flight envelope from an advance ratio of 0.4 to an advance ratio of 1. This investigation will supply information to be utilized in the construction of a high-speed, high-endurance quad-rotor biplane micro air vehicle.
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... The University of Maryland has been actively researching a quadrotor biplane tailsitter (QBiT) UAS configuration. They have manufactured scaled designs under 1 lb [3], as well as in the 6-8 lb range [4,5]. These aircraft have demonstrated interesting control problems, including a lack of roll authority in forward flight (which was solved by canting the rotors in [4]), as well as the availability of control redundancy with the inclusion of both RPM control and blade pitch control [5]. ...
... They have manufactured scaled designs under 1 lb [3], as well as in the 6-8 lb range [4,5]. These aircraft have demonstrated interesting control problems, including a lack of roll authority in forward flight (which was solved by canting the rotors in [4]), as well as the availability of control redundancy with the inclusion of both RPM control and blade pitch control [5]. Industry partners like Bell have also demonstrated interest in this configuration, with the Autonomous Pod Transport (APT) intended to scale from payload capacities of 70 lb to 1,000 lb [6]. ...
... powerplant selection). Concurrently with the development of the QBiT platforms in [3][4][5], researchers at the University of Maryland and ARL have been producing a physics-based design optimization tool called Hybrid Design and Rotorcraft Analysis (HYDRA) [8,9]. This tool has been used to produce a set of three scaled preliminary designs for the QBiT, which were optimized to perform a specific ferrying mission with as much payload as possible. ...
... For simplicity, this tilt-wing design considers a four-bar linkage (Actuation 1) and a gear train (Actuation 2), as shown in Fig. 10, to be compared and analyzed to determine which has a greater performance. According to Asada and Youcef-Toumi 22 , gear trains that are used for actuation mechanisms tend to suffer from backlash. Large preloading can be used to eliminate the backlash, but by doing this large friction occurs and wears the gears. ...
... Large preloading can be used to eliminate the backlash, but by doing this large friction occurs and wears the gears. Using a four-bar linkage eliminates backlash, has low friction, and has high mechanical stiffness 22 . To be able to accurately test the performance of the actuation mechanism, an experimental method must be proposed. ...
... However, they are now included in the conceptual design [3,4] of new configurationsairplanes with nonplanar wings [5], biplanes, box-wings [6,7], joined-wings [8], and wing tip devices [6][7][8][9], among others-for future use in commercial aircraft [10][11][12][13][14][15][16][17] in the design of RPAS (remotely piloted aircraft systems) [18][19][20][21][22]. The nature of RPAS, that is, an air vehicle without a pilot onboard, obviously allows for the possibility of dramatically reducing the size of the vehicles. ...
This paper presents a study based on wind tunnel research on biplane configurations. The objective of this research is to establish an experimental basis for relationships between the main geometrical parameters that define a biplane configuration (stagger, decalage, gap, and sweep angle) and the aerodynamic characteristics (CL, CD). This experimental study focuses on a 2D approach. This method is the first step towards dealing with the issue, and it allows the variables involved in the tests to be reduced. The biplane configuration has been compared with the monoplane configuration to analyze the viability for implementing the biplane configuration in the field of application for micro air vehicles (MAV). At present, the biplane and other unusual configurations have not been a common design for MAV; however, they do have unlimited future potential. A set of experimental tests were carried out on various biplane configurations at low Reynolds numbers, which allowed the criteria for selecting the best wing configuration to be defined. The results obtained here show that the biplane configuration provides a higher maximum lift coefficient (CLmax) than the planar wing (monoplane). Furthermore, it has a larger wetted surface than the planar configuration, so the parasitic drag increases for the biplane configuration. This research is focused on a drone flight regime (low Reynolds number), and in this case, the parasitic drag (profile drag) has an important role in the total drag of the airplane. This study considers whether the reduction in the induced drag due to three–dimensional configuration (biplanes, box–wings, and joined–wings) can reduce the total drag or if the increase in the parasitic drag is bigger. Additionally, the increase in lift and the decrease in parasitic drag (profile drag) will be studied to determine if they have a greater influence on the performance of the airplane than the increase in structural weight. Further research is planned to be performed on 3D prototypes, with the selected configurations, and applied to nonconventional wing planforms.
... Here we model the CRC-3 biplane tailsitter, depicted in Fig. 1. Each rotor is positioned with a 10 • inboard cant angle to increase maneuverability during wingborne flight [18]. We consider translation in the forward and upward axis directions only, and we limit rotation to occur only about the pitch axis. ...
Electric vertical takeoff and landing (eVTOL) aircraft take advantage of distributed electric propulsion as well as aerodynamic lifting surfaces to take off vertically and perform long-duration flights. Complex aerodynamic interactions and a hard-to-predict transition maneuver from hover to wing-borne flight are one challenge in their development. To address this, we compare three different interaction models of varying fidelity for optimizing the transition trajectory of a biplane tailsitter. The first model accounts for simplified rotor-on-wing interactions using momentum theory, while the other two account for wing-on-wing interactions using a vortex lattice method and rotor-on-wing aerodynamic interactions using blade element momentum theory. One includes the swirl component of velocity and the other neglects swirl. To determine the trajectory, we perform direct collocation on the lowest fidelity model using gradient-based optimization. To compare them, we use the same control inputs obtained in the optimization to integrate trajectories using the higher fidelity models. We find that the higher fidelity models predict power and stall significantly more conservatively than the lowest fidelity model. We conclude that modeling the swirl velocity of the rotor wake and the selected stall model play a significant role in defining the transition trajectory.
... The transition from hover to forward flight and back is also quite challenging for tailsitter designs as the entire vehicle has to maneuver by 90 • to change from hover to forward flight (Refs. [1][2][3][4]7,8). The quad-tiltrotor design (Ref. ...
This paper discusses the preliminary results from the experimental study of the aerodynamic performance of a novel multirotor tandem wing Unmanned Aerial Vehicle (UAV) during forward flight and transition to quantify the wing-wing and propeller-propeller interactions. The horizontal and vertical separations between the tandem wings are key design parameters for the current convertiplane configuration and are systematically identified through experiments performed in NWTF wind tunnel at Indian Institute of Technology Kanpur. For this a "half model" of the actual UAV wing is fabricated using 3D printing and tested at different wind speeds and angles-of-attack. For the baseline horizontal separation of 50% of wingspan and no vertical separation the ideal combination of wing setting angle is identified to be 3 • for fore wing and 6 • for the aft wing, as this combination offsets the downwash effect of fore wing on the aft wing with increased angle-of-attack and also takes advantage of the upwash of the aft wing to enhance the lift on the fore wing. A horizontal spacing equal to at least 50% of span is observed to give good performance for both the fore and aft wings. The vertical separation enhances the lift on the aft wing significantly. A vertical spacing of 30% of the wingspan helps minimize the interference between the wings and the propellers.
... A more efficient solution has been developed at University of Maryland, which is a quadrotor biplane MAV [10,11,12]. The design tries to overcome the mechanical complexity associated with tilting of rotors and wings in tiltrotor or tiltwing type hybrid concepts by making use of the maneuverability of the vehicle for transition. ...
This paper discusses the conceptual design and proof-of-concept flight demonstration of a novel variable pitch quadrotor biplane Unmanned Aerial Vehicle concept for payload delivery. The proposed design combines vertical takeoff and landing (VTOL), precise hover capabilities of a quadrotor helicopter and high range, endurance and high forward cruise speed characteristics of a fixed wing aircraft. The proposed UAV is designed for a mission requirement of carrying and delivering 6 kg payload to a destination at 16 km from the point of origin. First, the design of proprotors is carried out using a physics based modified Blade Element Momentum Theory (BEMT) analysis, which is validated using experimental data generated for the purpose. Proprotors have conflicting requirement for optimal hover and forward flight performance. Next, the biplane wings are designed using simple lifting line theory. The airframe design is followed by power plant selection and transmission design. Finally, weight estimation is carried out to complete the design process. The proprotor design with 24 deg preset angle and -24 deg twist is designed based on 70% weightage to forward flight and 30% weightage to hovering flight conditions. The operating RPM of the proprotors is reduced from 3200 during hover to 2000 during forward flight to ensure optimal performance during cruise flight. The estimated power consumption during forward flight mode is 64% less than that required for hover, establishing the benefit of this hybrid concept. A proof-of-concept scaled prototype is fabricated using commercial-off-the-shelf parts. A PID controller is developed and implemented on the PixHawk board to enable stable hovering flight and attitude tracking.
... Their work focused on the aerodynamic design of the airfoils and they implemented a quaternion based controller that operated in the hover and forward flight regimes. In a related work [25], Bogdanowicz et al. further developed the vehicle design to improve the roll authority provided during the forward flight regime. These works demonstrate the efficacy of a quadrotor bi-plane design. ...
... Also, the design facilitates easier transition, because significant portion of the wing remains straight at all times. A more efficient hybrid UAV solution has been developed at University of Maryland, which is a quadrotor biplane tail-sitter micro air vehicle [12,14,15]. The design, in which two wings are attached in a biplane configuration to a conventional quadrotor consisting of counterrotating propellers, tries to overcome the lack of control authority of regular tail-sitter and mechanical complexity associated with tilting of rotors and wings in tiltrotor or tiltwing-type hybrid concepts by making use of the maneuverability of the vehicle for transition. ...
This paper presents the development of 6-degrees-of-freedom (6-DOF) flight dynamics model and nonlinear control design for a novel hybrid biplane-quadrotor unmanned aerial vehicle capable of efficient operation in both vertical takeoff and landing (VTOL) mode and forward flight mode. The development of vehicle dynamics model considers a complete description of flight dynamics, wing aerodynamics, and prop wash modeling. Rotor and wing aerodynamics during hover, transition, and forward flight are the key components of the vehicle dynamics equations and are systematically validated with experimental data available in the literature. The rotor aerodynamic loads calculated using blade element theory and uniform inflow–based model is found to offer adequate fidelity during both axial and edgewise flights of the rotor. The rigid body rotation of 90° about pitch axis during transition from hover to forward flight and back necessitates the use of quaternions for representation of the attitude of the vehicle to avoid singularity associated with Euler angles for such maneuvers. A comprehensive nonlinear control design using dynamic inversion approach is developed for the whole flight regime that includes climb/descent, hover, transition, and forward flight. The performance of the proposed control design is demonstrated through numerical simulations on the 6-DOF model of the vehicle.
... A more efficient solution has been developed at University of Maryland, which is a quadrotor biplane MAV. [8][9][10] The design tries to overcome the mechanical complexity associated with tliting of rotors and wings in tiltrotor or tiltwing type hybrid concepts by making use of the maneuverability of the vehicle for transition. It consists of counter-rotating propellers arranged in a conventional quadrotor configuration, to which are attached two wings in biplane configuration. ...
Hybrid air vehicles can be very useful to perform tasks that require hover and forward flight capability. This paper describes the control development of a quadrotor-biplane hybrid air vehicle to enable transition from hover to forward flight mode. The vehicle weighs about 230 grams with biplane wings that have a span and chord of 26 inches and 4 inches respectively and are spaced about 10 inches apart. A linear quaternion based controller is setup that attempts to control the vehicle transition state through commands of specific desired quaternions. The performance of the controller was first tested through simulation studies, followed by bench-top experimental tests and finally free flight tests. Satisfactory controller performance in executing transition maneuvers through step changes in desired pitch angles (0 deg for hover, 90 deg for forward flight) was observed in simulation The controller was also seen to have acceptable disturbance rejection characteristics. Bench-top experiments showed satisfactory transition response to step and ramp changes in desired transition angles. A settling time of less than 2 seconds was observed in the controller response to a transition command. A fan-bank setup was setup to provide a varying dynamic pressure environment that the vehicle would encounter during transition. The control input power required to perform transition was about 5 times that required with no external wind conditions. This was within 15% of the maximum control power which suggests adequate control authority. Finally, successful transition flight tests were performed with an average velocity of 7 m/s in forward flight mode.
This paper discusses the design, hardware and software methodology, and testing of an ultralight inertial navigation system (ELKA-R) that can be used as a controller in a wide range of micro air vehicle (MAV) systems. ELKA-R was designed using the 32-bit low-power ARM Cortex-M4 microprocessor as the microcontroller unit (MCU). The MCU interfaced with state of the art 9 DOF (degrees-of-freedom) inertial measurment unit using inter-integrated circuit communication (I 2 C) protocol. A wireless transceiver was also incorporated with serial protocol interface (SPI) to wirelessly coordinate pilot inputs and sensor information with a remote basestation. Multiple timer protocols were configured to generate individual driver signals to a wide variety of motor and actuator configurations. The printed circuit board was designed as a four layer layout. ELKA-R weighed 1.7 grams with a board area of 4.82cm 2 thus making it one of the smallest and lightest kinematic autopilots in open literature that can be applied to any generic micro air vehicle system. ELKA-R was tested on a variety of MAV flight demonstrators. Hover stabilization rates of 1000 Hz were achieved which were comparable to the autopilot systems on larger quad rotor systems such as DJI Phantom and AR-Drone. Oscillations in attitude were reduced by up to 50-70% when compared with a previous generation lightweight autopilot.
Hover and forward flight capability can be combined in hybrid air vehicle designs such as a quad rotor biplane which is investigated in this paper. The vehicle weighs 240 grams and consists of four propellers with wings arranged in biplane configuration. To measure aerodynamic performance of the vehicle to maintain equilibrium during transition, a wing-propeller system that represents one quarter of the vehicle was used. Wind tunnel tests were performed on a single 6 in, two bladed propeller attached to a wing surface with an aspect ratio of 2.75. Tests were performed first on an isolated propeller at various shaft angles, RPM and forward flight velocity. The combined wing-propeller system was then tested to study key differences in force production with and without the wing surface. Finally trim analysis based on force measurements was performed to extract operating conditions for trimmed flight at flight modes including transition from hover to forward flight. Due to the effect of the wing on propeller slipstream and vice versa, the vertical force was greater, and the horizontal force was lower than that produced by the isolated propeller. A maximum speed of 11 m/s at 0 deg shaft angle was obtained with a cruise speed of about 6 m/s with a lift requirement of 0.6 N. The cruise power was 1.5 W which was one-third of hover power. Free flight testing successfully showed feasibility of vehicle to achieve equilibrium transition flight. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Since October 2005, the T-wing tail-sitter unmanned air vehicle has undergone an extensive program of flight tests, resulting in a total of more than 50 flights, many under autonomous control from takeoff to landing. Starting in August 2006, free flights with conversion between vertical and horizontal flight modes have also been undertaken. Although the latter flights have required some guidance-level ground-pilot input, significant portions of them were performed in autonomous mode, including the transitions between horizontal and vertical flight. This paper considers the overall control architecture of the vehicle, including the different control modes that the vehicle was flown under during the recent series of tests. Although the individual controllers for each flight mode are unremarkable in themselves, it is notable that the aggregate system allows the vehicle to fly throughout its entire flight envelope, which is considerably broader than that of conventional fixed- or rotary-wing vehicles. The performance of the controllers for the different flight modes will also be considered, with a particular focus on hover dispersion results, in differing wind conditions. The majority of these flights were performed on a tether test rig during autonomous control development, to ensure vehicle safety with minimal impact on vehicle dynamics. The demonstration of autonomous flight under the constraints imposed by the tether system in winds up to 18 kt is a significant achievement. Results from the more recent horizontal flight tests with conversions between vertical and horizontal flight are also presented. Most important, these results confirm the basic feasibility of tail-sitter vehicles that use control surfaces submerged in propeller wash for vertical flight control.
This paper presents vehicle models and test flight results for an autonomous fixed-wing airplane that is designed to take-off, hover, transition to and from level-flight modes, and perch on a vertical landing platform in a highly space constrained environment. By enabling a fixed-wing UAV to achieve these feats, the speed and range of a fixed-wing aircraft in level flight are complimented by hover capabilities that were typically limited to rotorcraft. Flight and perch landing results are presented. This capability significantly eases support and maintenance of the vehicle. All of the flights presented in this paper are performed using the MIT Real-time Autonomous Vehicle indoor test ENvironment (RAVEN). AFOSR Grant FA9550-04-1-0458 The Boeing Company
Wind tunnel testing was performed on a VTOL aircraft in order to characterize longitudinal flight behavior during an equilibrium transition between vertical and horizontal flight modes. Trim values for airspeed, pitch, motor speed and elevator position were determined. Data was collected by independently varying the trim parameters, and stability and control derivatives were identified as functions of the trim pitch angle. A linear fractional representation model was then proposed, along with several methods to improve longitudinal control of the aircraft.
In this paper, we propose an autonomous attitude control of a quad tilt wing-unmanned aerial vehicle (QTW-UAV). A QTW-UAV can achieve vertical takeoff and landing; further, hovering flight, which are characteristic of rotary-wing aircraft such as helicopter. And high cruising speeds, which is a characteristic of fixed-wing aircraft, can be also achieved by changing the angle of the rotors and wings by a tilt mechanism. First, we construct an attitude model of the QTW-UAV by using the identification method. We then design the attitude control system with a Kalman filter-based linear quadratic integral (LQI) control method; the experiment results show that a model-based control design is very useful for the autonomous control of a QTW-UAV.
A new design for a tail-sitter vertical takeoff and landing unmanned aerial vehicle was proposed. A nonlinear mathematical model of the vehicle dynamics was constructed by combining simple estimation methods. The flight characteristics were revealed through a trim analysis and an optimized transitional flight path analysis by using the mathematical model. The trim analysis revealed the existence of a flight path constraint to avoid stall; the vehicle could not descend in low-speed flight without high-lift devices such as flaps and slats. These devices improved the descent performance. In particular, slats provided a substantial improvement; they enabled a descent rate of 2 m/s. In the optimized transitional flight path analysis, a level outbound transition without high-lift devices was achieved although a trimmed level flight at low speed, as was shown in the trim analysis, was not possible; this was because the outbound transition was an accelerative flight. On the contrary, without high-lift devices, the vehicle could not avoid climbing to avoid stall during inbound transitions. The slats provided a satisfactory improvement during the transition and enabled a level inbound transition. These results showed the necessity of leading-edge slats for the proposed tail-sitter vertical takeoff and landing unmanned aerial vehicle.
Design and Control of a Tilt-Wing Micro Air Vehicle in Hover
- V Hrishikeshavan
- I Chopra
Hrishikeshavan, V., and Chopra, I., "Design and Control of
a Tilt-Wing Micro Air Vehicle in Hover," American
Helicopter Society 68 th Annual Forum, Fort Worth, Texas,
May 2012.
Control of a Quad Rotor Biplane Micro Air Vehicle in Transition from Hover to Forward Flight
- V Hrishikeshavan
- D Bawek
- O Rand
- I Chopra
8 Hrishikeshavan, V., Bawek, D., Rand, O., and Chopra, I.,
" Control of a Quad Rotor Biplane Micro Air Vehicle in
Transition from Hover to Forward Flight, " American
Helicopter Society Specialists' Meeting on Unmanned
Rotorcraft, Scottsdale, AZ, Jan 2013.